1. Field of the Invention
This invention relates to communication networks, and particularly to a network that provides portable users with secure access when exchanging information with other users on the network.
2. Discussion of the Known Art
As military conflicts are being resolved more through the use of a network-centric rather than a platform-centric paradigm, vital communications over the established networks must be secure, reliable, interoperative, survivable, and timely. The implementation of a high capacity, multimedia network is also desirable.
Free space optical (FSO) or photonic communication links have been deployed in fixed, point-to-point links for commercial and military applications. Such links may be preferred over microwave or millimeter wavelength radio frequency (RF) links for short range communications, especially when other communication infrastructure is unavailable, unreliable, or untrustworthy. FSO links have the following advantages:
1. The links are highly directional, and therefore quite immune to interception, interference or jamming.
2. Secure communications during periods of radio silence.
3. Elimination of any detectable RF signature.
4. FSO terminals can be made small, lightweight, and are easily portable. Optical antennas including light emitters (e.g., laser LEDs) and detectors (e.g., photodiodes) have typical gains on the order of one million times those of isotropic RF antennas.
5. Low power consumption.
6. The availability of a wide frequency spectrum with no governmental regulatory restrictions.
7. Large data bandwidth capacity.
8. Direct baseband signaling, thus simplifying modulation and demodulation processes.
9. Ease of multiplexing, de-multiplexing, and switching of optical channels.
10. Tactically useful range.
Projects are being pursued that would enable laser communication on the move between platforms ground to ground, ground to air, air to air, air to satellite, and satellite to air. Infrared (IR) light sources and detectors suitable for use in high data rate FSO transmitters and receivers are commercially available at low cost.
IR light penetrates clear glass but will not propagate through walls or other opaque building structures. FSO links are therefore confined to rooms or other areas inside buildings where the links are established. Such confinement enhances the security of FSO transmissions against interception or casual eavesdropping, and avoids interference between optical links operating in physically separate regions, thus making possible a high degree of spectrum reuse. Also, while multipath fading may cause signals to fluctuate in strength and phase over RF links, FSO links are immune to fading if intensity modulation and direct detection (IM/DD) techniques are applied. See, J. M. Kahn et al., “Wireless Infrared Communications”, 85 (2) Proceedings of the IEEE (Feb. 1997), at 265-98, which is incorporated by reference.
Portable Infrared (IR) Devices
For short range (up to a few meters) applications, consumer devices are available that allow data to be transferred between the devices via infrared light. The Infrared Data Association (IrDA) defines specifications for point-to-point communication using directional half duplex serial IR links through space, at data rates up to and including 115.2 kbit/s; 0.576 Mbps, 1.152 Mbps, 4.0 Mbps and 16 Mbps. Cell phones are available with IR ports that follow these standards for enabling the phones to dump data into stationary printers, PDAs, or PCs equipped with IR ports. See “Motorola i930/i920”, at <www.phonescoop.com/phones/phone.php?p=627>. IR ports of typical cell phones do not carry active voice communications and, as mentioned, are limited in range to 1 to 2 meters.
VoIP Telephony and Wireless Local Area Networks
The use of voice-over-Internet protocol (VoIP) telephony, both wired and RF wireless, is expanding. In a conventional circuit switched telephone system, a dedicated physical connection is established between a calling and a called party over the duration of the call. The continuous connection assures that voice signals carried between end points of the system are not interrupted. With a VoIP system, however, there is no dedicated connection. Instead, analog voice signals from a microphone transducer in a user's handset or headset are digitized, and corresponding digital data is transmitted over a system network in separate groups of data called “packets”. Each packet contains the sender's and the recipient's IP addresses, and a piece of digitized voice information (“payload” data). The packets may be routed through the network over different paths, and eventually arrive with some delay at a common destination to be recombined in the proper sequence. Further, each packet may arrive with a different delay. Variations in arrival time are defined as “jitter”. Some packets may never reach the destination, resulting in “packet loss”. Most vendors adhere to strict limits on tolerable packet loss, delay, and jitter. For example, Cisco Systems adopted the following guidelines for VoIP network operation:
Network PerformanceValueDelay<=150 milliseconds (ms) one-wayJitter<=30 msPacket loss<=1%
VoIP may offer many features above and beyond those afforded by traditional telephony systems, whether wired or remote. See, e.g., A. Noser, “Combining VoIP and Wireless Services”, at <www.ncstate.net/wireless/presentations/wirelessvoip/wirelessvoip.html>, which is incorporated by reference. Manufacturers claim their wireless VoIP products allow mobile users to engage in conversations anywhere in an IP network with reliability and voice quality equivalent to that of a desktop office phone. Internet gateways and RF access points are positioned to ensure that user conversations do not drop out or experience gaps, regardless of a user's location within a defined area. As voice quality, reliability and security improve, IP wireless communication including the use of convenient portable VoIP handsets is likely to increase.
A typical VoIP local area network (LAN) 10 is illustrated in FIG. 1 including commercial off-the-shelf (COTS) products. To connect with a legacy public telephone switching exchange (PBX) 12, a telephony gateway 14 is configured to convert analog voice signals received over the PBX 12 into IP voice data packets. The packets are routed through an Ethernet cable 15 that connects with RF wireless access points 16. Voice data packets arriving at the gateway 14 over the cable 15 are converted to analog voice signals for transmission into the PBX 12. The gateway 14 may be omitted if the PBX 12 is a so-called telephony server.
The access points 16 may comprise RF wireless routers each of which operates according to, e.g., known IEEE 802.11x signaling protocols. A voice priority server 20 available, for example, from Spectralink SVP® may be provided to ensure that the voice data packets have priority over other kinds of data carried over the network 10. The access points 16 may join or bridge various wireless clients such as, for example, a number of portable VoIP telephone sets 26, a notebook computer 27 and a PDA 28, with fixed users and devices connected by wire to the network 10.
FIG. 2 shows a typical high level architecture for a wireless access point 16. Access point 16 may operate, for example, under one or more defined RF signaling protocols per the IEEE Standards 802.xxx. Because voice data transmitted by a user of a RF device may be received by users of like RF devices within range, some security measures are available to ensure that a user's data is not captured or manipulated by unauthorized intruders. When classified or other highly sensitive voice messages are involved, however, commercial security (COMSEC) is insufficient for the task. For example, adding improved Type I security can significantly increase cost and management complexity, since such security must be controlled and crypto keys must be managed.
Wireless VoIP Phone Sets
Several vendors provide RF wireless VoIP telephone sets that can access a LAN using IEEE 802.11x or other newly emerging IEEE 802.xxx RF signaling protocols. For example, a model WIP330 Wireless-G IP Phone from Linksys. A block diagram of a typical wireless VoIP telephone 26 is shown in FIG. 3. Core subsystems include:
An RF transceiver/power amplifier 30 that performs frequency translation between the RF and the baseband (voice) signals, and amplifies RF signals to be radiated from the phone from an antenna 31.
A medium access control (MAC)/baseband processor 32 which implements the applicable IEEE 802.xxx protocols and provides modem functionality to control wireless signaling and communication between the telephone 26 and the wireless access points of the LAN.
A DSP/microcontroller/OMAP 34 that executes VoIP call controls and voice processing, and provides a user interface.
Various memories including flash, ROM and RAM stages for storing programming code, voice and other data.
A voice coder-decoder (CODEC) 36 which interfaces with a user headset 37 having a microphone 38 and a speaker or earpiece 39. The CODEC 36 operates to convert a user's analog voice signals as produced by the microphone 38, into corresponding digital voice data to be processed by the OMAP 34.
The RF bandwidth required for each voice call depends on (i) the type of CODEC 36, (ii) the number of CODEC samples per data packet, and (iii) the packet header compression. The number of CODEC samples per packet affects the delay of a VoIP call. As the size of the sample data increases, the required bandwidth decreases but the overall delay increases.
As mentioned, if a wireless VoIP telephone set user desires to discuss classified subject matter, COMSEC items must be provided thereby increasing equipment cost and management complexity. Accordingly, there is a need for a robust multi-user local area wireless network that is not only capable of interfacing with current VoIP telephone sets, but which also provides security for portable users who want to convey sensitive information without having to invoke costly COMSEC measures.